A position-measuring device is described, for example, in U.S. Patent Application Publication No. 2005/023450. In addition to a measuring grating, e.g., taking the form of a linear reflection measuring grating, it includes a scanning unit displaceable relative thereto in at least one measuring direction. Provided on the side of the scanning unit are a primary light source as well as at least one detector assembly in the form of a periodic detector array. In the event a spatially extended primary light source is used, a periodic configuration of point light sources is able to be generated in the detection plane by disposing what is termed a transmitting grating in this plane. The transmitting grating is made up of a periodic arrangement of light-transmitting and opaque regions in the measuring direction.
In the event of the relative movement of the scanning unit and measuring grating, a stripe pattern, modulated as a function of the displacement, results in the detection plane and is detected by the detector assembly and converted into scanning signals able to be further processed. In this context, because the detector assembly is in the form of a periodic detector array, a plurality of phase-shifted scanning signals is generated in customary manner.
In such systems, as a rule, the aim is for the primary light source used and the detector assembly employed to be situated in the same plane to the greatest extent possible. This ensures that the distance between the primary light source and the measuring grating is identical to the distance between the measuring grating and the detector assembly. To that end, the primary light source according to U.S. Patent Application Publication No. 2005/023450 is situated below the transmitting grating in a central cavity in a carrier substrate. The cavity is surrounded by the detector elements of the detector array. However, such a configuration is associated with significant manufacturing costs. Thus, the carrier substrate must be formed with a suitable cavity; in addition, the contacting of the primary light source in the cavity proves to be relatively difficult.
Therefore, German Published Patent Application No. 10 2006 021 017 describes placing the primary light source at a different location in the scanning unit. In the scanning beam path, a suitable reflector element is provided, via which the primary light source is imaged into a virtual light source in the detection plane. In this manner, the formation of a cavity may be avoided, and more varied possibilities are obtained for placing the primary light source in the scanning unit.
The measures described in German Published Patent Application No. 10 2006 021 017 are suited for solving the problems in connection with the cavity if point light sources, for instance, what are referred to as VCSEL light sources, are used as primary light sources. If such point light sources are not available and spatially extended primary light sources, e.g., LEDs, must be used, then the measures described in German Published Patent Application No. 10 2006 021 017 are not sufficient to ensure reliable generation of position-dependent scanning signals.